Video.
My previous attempts were at an even slower downward speed. Trust me not to realise it was faster when the camera was rolling.
That’s what comes of doing it in cramped space … neighbour’s garage to the right, my fence in front, parked Shogun to the left, friend’s car behind. 
Even so, the downward movement isn’t fast.
But - it gives you the info you need. Beware bobbing boats!
